The song 'Birds of a Feather' by Billie Eilish expresses a deep commitment and love towards someone, symbolized by staying together until death. The lyrics convey a sense of loyalty, devotion, and a desire for eternal connection, even in the face of challenges and uncertainties. The metaphor of 'Birds of a Feather' emphasizes the idea of unity and sticking together through thick and thin, highlighting the bond shared between the singer and the person they love.